1. Field of the Invention
The present invention relates to an inverter-integrated electric compressor that is particularly suitable for use in an air-conditioner apparatus of a vehicle.
This application is based on Japanese Patent Applications Nos. 2006-315771 and 2006-315772, the contents of which are incorporated herein by reference.
2. Description of Related Art
Currently, the automobile industry is rapidly promoting the development and commercialization of electrically driven vehicles, such as hybrid vehicles, electric vehicles, and fuel-cell-powered vehicles, to improve energy efficiency.
These vehicles employ air-conditioner apparatuses that, unlike conventional air-conditioner apparatuses, are provided with electric compressors driven by electrically powered motors.
These electric compressors are encapsulated electric compressors having a compressor and an electric motor in a housing and convert direct-current power from the power supply into three-phase alternating-current power via an inverter apparatus. The three-phase alternating-current power is supplied to the electric motor so that the rotational speed in the compressor can be variably controlled according to the air-conditioning load.
For such inverter-driven electric compressors, there have been proposed many inverter-integrated electric compressors that integrate inverter apparatuses with housings thereof.
For example, Japanese Unexamined Patent Application, Publication No. 2004-190547 proposes an inverter-integrated electric compressor that includes an inverter assembly composed of a metal base plate, a power semiconductor module, a smoothing capacitor, a busbar assembly, and a printed substrate, in which an inverter apparatus is integrated with the electric compressor by securing the base plate of the inverter assembly on the circumferential top surface of the housing of the electric compressor.
In addition, Publication of Japanese Patent No. 3760887 proposes an inverter-integrated electric compressor that includes, on a flat base surface of the outer circumferential surface of a motor housing, six power MOS transistor modules (power semiconductor switching elements) constituting upper-arm switching elements and lower-arm switching elements for the three phases of a three-phase inverter such that these six power MOS transistor modules are arranged side by side in three columns in the motor shaft direction and in two rows in the radial direction to allow one set of the three power MOS transistor modules in the radial direction to serve as the upper-arm switching elements and the other set of the three power MOS transistor modules in the radial direction to serve as the lower-arm switching elements.
For such an inverter apparatus that is integrated with the outer circumference of the housing of an electric compressor for integration with the electric compressor, it is necessary to take measures to cool power semiconductor modules, which generate heat, such as Insulated Gate Bipolar Transistors (IGBTs), and to take measures to ensure the ability to withstand vibrations from the vehicle in which the electric compressor is mounted.
These heat-generating elements are typically cooled by using the above-described metal base plate (aluminum plate) serving as a heatsink and by drawing upon the endothermic effect of low-temperature refrigerant gas flowing in the housing of the electric compressor.
As far as vibration is concerned, in view of minimizing cost and weight, vibration resistance is increased by firmly securing a metal base plate made of an aluminum alloy to the housing with screws at a plurality of (normally four) locations, thereby increasing the natural frequency.
When mounted in a vehicle, such an inverter-integrated electric compressor is typically oriented such that the motor shaft direction is parallel to the front/back direction of the vehicle, and one side surface of the inverter-integrated electric compressor is bolted onto a bracket which is fixed, for example, on a side surface of the prime mover at three locations, two in the lower part and one in the upper part. For this reason, vertical vibration from the vehicle is applied to the inverter-integrated electric compressor as vibration around the motor shaft, which possibly causes the inverter apparatus to resonate with the vibration via the metal base plate.
Countermeasures against this resonance include increasing stiffness by using a thick metal base plate or increasing the number of fixing positions on the housing. Simply making the metal base plate thicker or increasing the number of bolts, however, is not desirable because doing so would adversely affect the capability to cool the heat-generating elements, the reduction in weight, and the ease of assembly. Thus, vibration of inverter apparatuses remains a problem which must be solved.
Furthermore, for the power MOS transistor modules in the inverter apparatus of the inverter-integrated electric compressor described in the above-described Publication of Japanese Patent No. 3760887, the surrounding wall of the motor housing is used as a heatsink, and heat generated by these power MOS transistor modules is released to refrigerant gas flowing in the motor housing. In this manner, a compact and lightweight inverter apparatus is realized, and the heat-dissipating resistance is reduced to achieve effective cooling of the inverter apparatus.
With the above-described layout of the power MOS transistor modules, however, it is not possible to uniformly cool the upper-arm U-V-W phase-switching elements and the lower-arm U-V-W phase-switching elements due to the manner in which the refrigerant gas flows in the motor housing. Due to this, the phase-switching elements are cooled differently from each other, which may lead to unstable operation of the inverter apparatus.